Catalytic processes for the conversion of hydrocarbons using platinum group metals and a catalyst support are well known and extensively used. One such process is catalytic reforming of naphtha wherein the naphtha is co-processed with hydrogen over platinum containing reforming catalysts. During naphtha reforming, the catalysts used in these processes become deactivated. Often the accumulation of coke deposits causes the deactivation. Reconditioning of the catalyst to remove coke deposits is necessary to restore the activity of the catalyst. Coke is normally removed from catalyst by contact of the coke containing catalyst at high temperature with an oxygen-containing gas to combust and convert coke to essentially carbon dioxide and water in a regeneration process. Equipment and technology for continuously or semi-continuously removing catalyst particles from a reaction zone and for coke removal in a regeneration zone are well known.
In order to combust coke in a typical regeneration zone, a regeneration gas is continuously circulated to the burn zone of a regeneration section and a flue gas containing by-products of coke combustion, oxygen and water is continually withdrawn. Coke combustion is controlled by using low oxygen concentration regeneration gas to contact the coke-containing catalyst particles. The regeneration gas is continuously circulated through the catalyst particles in a recycle gas loop. A small stream of combustion gas is added to the regeneration so as to replace oxygen consumed in the combustion of coke and a small amount of flue gas is vented off to allow for the addition of the combustion gas. The steady addition of combustion gas and the venting of flue gas establish steady state condition that produces a nearly constant concentration of water and oxygen in the regeneration gas.
After the burn zone, the metal-containing catalyst particles drop to a halogenation zone. Chlorine or other halogen-containing gas circulates through the halogenation zone in a halogenation loop. Contacting the catalyst with the haolgenation gas redisperses platinum group metals on the catalyst particles. In addition, some of the added halogen replaces lost halogen from the catalyst during naphtha processing. The halogen gas added to the halogenation loop sometimes enters the loop in admixture with air or other oxygen-containing gas. The process in the halogenation zone enables re-dispersion of the platinum group metals on the catalyst and it is referred to as white burn when used after the regenerator burn zone described previously
From the halogenation zone catalyst particles descend into a drying zone. A heated gas contacts the catalyst particles and drives moisture from the catalyst. Typically, air or an oxygen-containing gas enters the drying zone as the drying medium and passes upward through the halogenation zone to the burn zone to provide combustion gas.
The three different zones provide three potential places for the introduction of air or an oxygen-containing gas into the regeneration system. These three locations are often referred to as upper, middle and lower air and correspond to the relative positions of the upper burn zone, middle halogenation zone, and lower drying zone. When coke on the spent catalyst is low, the regenerator is not used and catalyst is not usually circulated. The performance of the catalyst in the reactors decline with time as re-activated catalyst particles are not continuously introduced to replace spent catalyst. Long term continuous operation of the reformer in this mode without the use of the regenerator leads to inefficient and uneconomical naphtha reforming.